1. Field of the Invention
The present invention relates generally to video tape recorders and more particularly to a helical scan video recorder of the EIAJ 2 type in which each field is recorded in segmented fashion onto a video tape.
2. Description of the Prior Art
A typical prior art video tape recorder of the EIAJ type two is the U-matic recorder designated 2850 by the Sony corporation. This recorder employs a pair of coaxially mounted cylindrical drums the top one of which is rotated at a speed of substantially 1800 RPM (where NTSC video signals are employed). Affixed to diametrically opposing points on a lower portion of the upper, rotating, drum are a pair of record/playback heads. Video recording tape normally housed in a tape cartridge is transported past the drums such that a portion of the tape is wrapped in proximity with just over 180.degree. of circumference of the drums. The tape is slightly skewed with respect to the drums such that the heads as they rotate transverse the width of the tape defining paths or tracks which cross the tape at an acute angle with respect to the length of the tape. The tape is transported past the drums by a capstan which maintains at high speed of approximately 400 inches per second at which speed gaps or guard bands are defined between successive tracks on the tape.
Video signals which are to be recorded onto the tape are processed by electronic circuits using the color under system. More specifically, the circuits separate the black and the white, or luminescence, information from the color, or chrominance, information. The luminescence informatation is used to FM modulate a carrier to produce a frequency modulated signal which deviates from approximately 3.5 to 5.5 megahertz. The chrominance information is used to amplitude modulate a 688 kilohertz carrier. The signals are then recombined, amplified and split into a pair of similar signals each of which drives a respective one of the drum mounted record/playback heads.
Additionally, the synchronization pulses of the video signal are compared with a tachometer signal derived from a sensor which monitors the rotating drum to generate a braking signal used to slow the speed of the drum. In this way, the drum and thus the record/playback head speed is maintained such that each head as it rotates through its respective half revolution, where it is in proximity to the tape, records one complete field of the video signal on a respective track of the tape.
During playback, the reproduced signal is decoded, recovering the luminance and chrominance information which are combined to develop a reproduced video signal. In addition, a 30 hertz synchronization signal is derived from the reproduced signal and used to synchronize the drum speed, and a 30 hertz signal recorded on a control track is used to control the capstan speed such that the heads are maintained in proper alignment with the tracks of the tape.
Although the quality of signals reproduced by the above-described recorder are of satisfactory quality for most applications they are not of sufficient quality to meet broadcast standards. Heretofore, in order to obtain signals of broadcast quality, it has been necessary to utilize a much more complex recorder which as a consequence of its complexity is typically not portable and an order of magnitude more expensive than EIAJ 2 recorders. Additionally, such recorders typically use tape which because of its width and the relative velocity at which it is transported is an order of magnitude more expensive than the tape used by the EIAJ 2 recorders.